Two cytoskeletal proteins from normal hamster fibroblasts will be purified and localized within the cell. The proteins have molecular weights of 52,000 and 55,000, respectively. They copurify with the 10 nm filament preparation of this cell line. The 55,000 dalton protein is analagous to "vimentin," the major form of the 10nm filament protein of fibroblasts. The second protein having a molecular weight of 52,000 is analagous to "desmin" the major form of the 10 nm filament protein of smooth muscle. These conclusions were based on a comparison of the two dimensional gel profiles and peptide maps of the fibroblast proteins to purified samples of vimentin and desmin. Antisera have been raised to these proteins and will be used to localize these proteins within the cell by means of indirect immunofluorescence.